ARID1A and epithelioid sarcoma: Loss of the expression of other SWI/SNF subunits, namely SMARCA4/BRG1, SMARCC1/BAF155, SMARCC2/BAF170 [98], or ARID1A/BAF250A [99], has been claimed as causative for the extremely rare SMARCB1-proficient ES cases in which SMARCB1/INI1 protein expression is retained (Figure 2).